Hunger, Thirst and Control of Food Intake Flashcards
State three triggers of thirst. Which is most potent?
Increase in plasma osmolality (most potent)
Decrease in blood volume
Decrease in blood pressure
Where are the osmoreceptors that trigger ADH release located?
OVLT - organum vasculosum
SFO - subfornical organ
These are found in the hypothalamus
How do the circumventricular organs detect changes in plasma osmolality?
They have an incomplete blood brain barrier so they can detect the changes taking place in the periphery - they are NOT isolated by the BBB.
The changes in plasma osmolality make the cells shrink or swell which signals to the ADH producing cells in the hypothalamus to change ADH release.
How come thirst is temporarily relieved when you drink water but before it has any effect on plasma osmolality?
There are receptors in the mouth, pharynx and oesophagus that are involved in this temporary relief of thirst.
What major hormone is involved in regulating thirst? What does it do?
Angiotensin II - it stimulates fluid retention
What neural and hormonal components have an effect on the hypothalamus in regulating hunger?
Neural - Vagal afferents
Hormonal - Ghrelin, PYY, Leptin
Which part of the brain is heavily involved in regulating hunger and what does it communicate with?
Arcuate nucleus
It is located beneath the 3rd ventricle and communicates with the paraventricular nucleus (above the 3rd ventricle)
What are the two groups of neuronal populations in this part of the brain and what effect does this have on hunger?
Stimulatory - NPY/Agrp
Inhibitory – POMC
What feature of the arcuate nucleus makes this good for regulating hunger?
It has an incomplete blood-brain barrier thus allowing access to peripheral hormones. It integrates peripheral and central feeding controls.
Describe the melanocortin system and how it regulates hunger.
POMC can be broken down to produce an anorectic hormone called alpha-MSH that agonises the melanocortin-4 receptor and suppresses food intake.
Agrp, also produced in the arcuate nucleus, can antagonise the MC4R receptor and make you feel hungry.
MC4R is in the paraventricular nucleus.
What mutations or deficiencies within this melanocortin system can cause obesity?
MC4R deficiency and POMC mutation
Where is leptin produced and what are its two roles?
Leptin is produced by adipocytes in white adipose tissue
Leptin tells the brain how much fat is stored and hence regulate food intake and regulates thermogenesis.
State three possible mechanisms that would make leptin responsible for obesity.
Absence of leptin - only seen in Congenital Leptin Deficiency which is a mutation in the ob gene
Regulatory defect - inability of the leptin stores to increase proportionally with increasing fat
Leptin resistance - problem with the hypothalamus, partially responsible for obesity
What determines the amount of PYY secreted?
The size of the meal
Describe the action of PYY.
PYY 3-36 travels to the arcuate nucleus and inhibits NPY release and stimulates POMC neurons so you DECREASE APPETITE.
